The invention is directed to a method and to an arrangement for channel allocation in a radio communication system, particularly in a radiotelephone system.
In radio communication systems, information such as, for example, voice, image information or other data are transmitted between a sending and a receiving radio station such as, for example, a base station or radio station with the assistance of electromagnetic waves via a radio interface. The emission of the electromagnetic waves thereby occurs with carrier frequencies that lie in the frequency band provided for the respective system. The carrier frequencies lie in the region of 900 MHz, 1800 MHz and 1900 MHz in GSM (Global System for Mobile communication) that is known from, among others, J. Biala, xe2x80x9cMobilfunk und Intelligente Netzexe2x80x9d, Vieweg Verlag, 1995. Frequencies in the frequency band of approximately 2000 MHz are provided for future mobile radiotelephone systems with CDMA or TD/CDMA transmission methods via the radio interface such as, for example, the UMTS (Universal Mobile Telecommunication System) or other systems of the 3rd generation.
The article by J. Mayer, J. Schlee, T. Weber, xe2x80x9cProtocol and Signalling Aspects of Joint Detection CDMAxe2x80x9d, PIMRC""97, Helsinki, 1997, pp. 867-871, discloses that respectively one or more traffic channels can be allocated to a communication connection on the basis of a channel pooling, whereby each traffic channel according to a CDMA transmission method can be distinguished by an individual CDMA code. The method of channel pooling is advantageously utilized in order to realize a communication connection to or from radio stations with different data rates or to be able to operate a plurality of services in parallel on one communication connection. A traffic channel, which is referred to simply as a channel in the rest of the specification, is thereby defined as a combination of a frequency channel, a time slot and a CDMA code. Instead of a permanently allocated frequency channel, time slot and CDMA code, a respective frequency skip sequence, time slot skip sequence or CDMA code skip sequence can also be employed as an alternative.
In the known mobile radiotelephone systems such as, for example, the GSM, signalling messages that are employed in a connection setup or in a handover contain information elements that specify the channel to be respectively allocated for the transmission of payload data. The connection setup and handover procedures are disclosed on pages 173-185 of the Prior Art of J. Biala. A separate information element for each channel to be designated is provided according to this system. Given a utilization of channel pooling in a TD/CDMA mobile radiotelephone system, a plurality of channels can be allocated to a radio station, whereby a midamble code must also be respectively additionally communicated in the upstream direction from the radio station to the base station. The use of the method of channel allocation known from the GSM mobile radiotelephone system with an information element for each channel to be allocated in a TD/CDMA mobile radiotelephone system would result in the occurrence of a very high signalling expense that disadvantageously limits the transmission capacity and the flexibility of the mobile radiotelephone system.
It is an object of the invention to specify a method that enables an allocation of a plurality of channels while avoiding a high signalling expense.
According to the method and system of the invention, for channel allocation in a radio communication system that uses a TD/CDMA subscriber separation method, an allocation of at least one channel from a sum of available channels is signaled to a radio station by an information element in a signaling message. At least one time slot from a fixed sum of time slots is selected by a time slot selection sub-information element in the information element. At least one CDMA code from a fixed sum of CDMA codes is subsequently selected for each selected time slot by a code selection sub-information element in the information element, whereby a number of code selection sub-information elements for the selection of the CDMA codes corresponds to the number of selected time slots.
In the method of the invention for channel allocation in the radio communication system that uses a TD/CDMA subscriber separation method, the allocation of at least one channel from a sum of available channels is signaled to a radio station by an information element in a signaling message. At least one time slot from a defined sum of time slots is selected in the information element with a time slot selection sub-information element. Subsequently, at least one CDMA code from a fixed sum of CDMA codes is selected by a code selection sub-information element for each selected time slot in the information element, whereby the plurality of code selection sub-information elements for the selection of the CDMA codes corresponds to the plurality of selected time slots.
Compared to the prior art, this method has the advantage that the radio station can have one or more channels in one or more time slots allocated to it with a single information element in a signaling message. The plurality of sub-information elements in the information element required for the selection of the time slots and of the CDMA codes is advantageously reduced in that the allocation of the channels occurs in down hierachic fashion in such a way that at least one time slot is selected first and at least one CDMA code is subsequently selected for each time slot. Due to the dependency on the respective time slot in the selection of the CDMA codes, the selected time slots need be defined in only one sub-information element. A great flexibility in the selection of the CDMA codes in the time slots is also advantageously assured, so that, for example, the plurality of selected CDMA codes in the respective time slots can vary.
In the method according to the invention for channel allocation in a radio communication system that uses a TD/CDMA subscriber separation method, the allocation of at least one channel from a sum of available channels is signaled to a radio station by an information element in a signaling message. At least one CDMA code from a fixed sum of CDMA codes is selected in the information element with a code selection sub-information element. Subsequently, at least one time slot from a fixed sum of time slots is selected in the information element with a time slot selection sub-information element, whereby the selected CDMA codes are employed in each selected time slot.
This method according to the invention has the advantage that, as a result of the hierarchic structure wherein one or more CDMA codes and, subsequently, one or more time slots are selected, the plurality of sub-information elements is minimized. By using the same CDMA code in a plurality of time slots, only respective a single code selection and time slot selection sub-information element is needed for a channel allocation.
According to a first development of the invention, a frequency channel for the upstream or downstream direction is additionally selected in the information element from a sum of frequency channels, being selected with a frequency channel selection sub-information element, whereby the number of time slots is referred to the selected frequency channel.
With reference to the first development of the invention and according to a second development, the allocation of additional channels in at least one further frequency channel to the radio station in the signaling message is signaled with an additional information element for each additional frequency channel, whereby the structure of the additional information element corresponds to that of the information element.
This feature makes it advantageously possible that a radio station that, as a result of its technical configuration, is in the position to send or to receive on a plurality of frequency channels can have channels in a plurality of frequency channels allocated to it in one signaling message. The allocation thereby in turn occurs in such a way that an information element or additional information element is provided for each frequency channel.
In accordance with a further development, the sum of the time slots is indicated in the information element with a sum time slot sub-information element and/or a sum of the CDMA codes for a time slot is indicated by a sum code sub-information element. Due to this embodiment, the plurality of time slots and/or the plurality of CDMA codes per time slot can be very flexibly adapted to the demands, for example with reference to the transmission capacity of a channel.
According to a further development of the invention, the sum of the midambles for the upstream direction is indicated in the information element by a sum midamble sub-information element, and one midamble is subsequently selected from the sub of midambles by a respective selection midamble sub-information element for each selected time slot. In this development, advantageously, only the common midamble is employed for all channels following a general definition of the plurality of midambles employed, for example, per frequency channel in each time slot in which CDMA codes were selected for the radio station. As a result thereof, the signaling expense in the allocation of the midambles is advantageously reduced, and the signal processing both in the radio station as well as in the base station is facilitated.
According to a further development of the invention, the plurality of channels to be allocated is determined by the radio station from a length of the information element. The radio station is thereby in the position to determine the plurality of channels to be allocated to it from the length of the sub-information elements.
With reference to the above development, the radio station in a further development is informed of the length of the information element by a length field, as a result whereof the radio station is already aware of the entire length of the information element before the beginning of the channel allocation. This advantageously serves for faster processing of the information contained in the information element by the radio station.
According to a further development of the invention, the channels for the upstream direction and for the downstream direction are allocated to the radio station independently of one another in the signaling message. As a result of this embodiment, asymmetrical data rates for the upstream and downstream direction can be advantageously achieved by the allocation of a respectively different plurality of channels.